In the course of converting the public power supply towards a supply which is increasingly oriented towards regenerative power supply, it proves to be increasingly important to react to short-term fluctuations in the electric supply network by provision of electric control reserves. Particularly when the public power demand rises above a base load for a short time, it is necessary the cover this additional energy demand by means of suitable medium-load or peak-load power plants.
Particularly the power supply when encountering short-term peak loads constitutes a huge challenge to the public power supply, however. For covering these short-term demand peaks, quickly controllable peak-load power plants are typically used. These can provide high electric outputs to the public electricity network within seconds or minutes and so cover the demand. Also, during network controlling, during which fluctuations in the case of changing power output demands in the public electricity network have to be compensated, power plant types which allow a high time dynamic with regard to their possible power output are required.
Pump-storage power plants or compressed air storage power plants inter alia are counted among conventional peak-load power plants. However, gas turbine power plants are also suitable for network control on account of their comparatively short startup times which lie within the range of a few minutes. Despite this flexibility with regard to the provision of electric energy, it is shown to be essential, however, to provide additional power supply devices which can cover a very short-term power demand. In this case, especially high-temperature batteries can play a large role and can provide power outputs to the public electricity network within the region of seconds. Moreover, such high-temperature batteries allow the electric temporary storage of surplus power from the public electricity network at times of over-production which in turn can be made available to the electricity network at times of increased power demand.
A battery type, the operating temperature of which lies above 100° C., preferably above 250° C., more preferably above 500° C. and most especially preferably above 600° C., is to be understood as a high-temperature battery in this case and in the following text. In particular, mention is to be made in this case of the sodium-sulfur accumulator which can be operated as a solid-electrolyte accumulator at operating temperatures of typically above 250° C. The typical operating temperatures of a sodium-sulfur accumulator lie between 250° C. and 350° C.
Most especially preferably, the high-temperature battery is also designed as a metal-air battery, as is described in detail in the laid-open publication DE 10 2009 057 720 A1, for example. This publication shall also be explicitly incorporated herewith by reference in the present case. The metal-air battery which is described therein is based on the use of a metal as a reducible chemical accumulator in combination with a process gas electrode which is typically supplied with oxygen, especially air oxygen, during operation. For the electrical separation of the process gas electrode, acting as a cathode during the discharging operation, from a metal-containing anode, provision is made for a solid electrolyte which conducts oxygen ions. Such a solid electrolyte can be yttrium-stabilized zirconium dioxide, for example. The solid electrolyte, on account of its selective ion conductivity, allows the transporting of oxygen ions from the cathode to the anode. At the same time, the solid electrolyte has electrical insulation properties which ensure that electrical charge carriers can flow from the anode to the cathode only via an external conductor. In order to be able to ensure a sufficient ion conductivity, it is necessary, however, to achieve an operating temperature of approximately 600° C. Typical operating temperatures lie between 600° C. and 800° C.
A disadvantage during operation of the above-described high-temperature batteries are their supply with sufficient thermal energy for achieving the necessary operating temperatures. In particular, the previously described metal-air battery, on account of its operating temperatures of typically at least 600° C., requires the provision of a large quantity of thermal power. This is typically provided via suitable electric heating elements, which in their turn are again operated by power from the public electricity networks. As a result of the additional demand for electric power, the overall efficiency of the high-temperature batteries is noticeably reduced, however. Since the high-temperature batteries, however, are to deliver electric power especially at times at which an increased power demand and a low power supply exist anyway, and consequently the electric power from the public electricity networks is comparatively expensive, an uneconomical operation results particularly at these operating times.